Abstraet. Free radical scavenging activities of wine samples were investigated by means of electron paramagnetic resonance (EPR) spin trapping. 1,l-Diphenyl-2-picrylhydrazyl served as a source of free radicals, "OH radicals were produced by the Fenton system, and in situ thermally generated SO 2" radicals from K2S20 s and carbon-centered radicals from azo-compounds were also used. 5,5-Dimethylpyrroline-N-oxide (DMPO) was used as a spin trapping agent. Three white and four red wine samples from the Slovak wine regions, along with 12% (v/v) aqueous ethanol solution as a reference sample, were compared. In general, the !owest scavenger activity was found in the reference sample, a higher one in the white, anda considerab[y higher one in the red wines, except when the Fenton system was used as the radical source. Here, unexpectedly, unlike in the other radical sources, the wine samples increased the yield of DMPO-adducts by about 5 times, compared to the reference sample. This is probably due to ah additional activation of the Fenton system by wine components. Higher concentrations of Mn '+ ions as determined by EPR spectroscopy corresponded to an increased scavenging activity of wines.

The thermally initiated decomposition of K2S2O8 radical initiator coupled with EPR spin trapping represents a very powerful source of reactive free radicals which can be effectively used to initiate and to monitor various radical processes, as we were able to demonstrate in the characterization of the antioxidant properties of wine samples. The spin trapping agent α‐phenyl‐N‐tert‐butylnitrone (PBN) is a very effective trap, but with low selectivity. 5,5‐Dimethyl‐1‐pyrroline‐N‐oxide (DMPO), which has higher selectivity and a very pronounced dependence of adduct formation on the temperature (the formal activation energy of ·DMPO–OH formation is 81.1 kJ mol−1), offers more advantages. In pure aqueous solutions, formation of the ·DMPO–OH adduct dominates. In mixed water–ethanol solvents, carbon‐centred DMPO radical adducts are increasingly evident with higher CH3CH2OH ratios, and at very high ethanol ratios the formation of ·DMPO–OOR adduct prevails. Copyright © 2000 John Wiley & Sons, Ltd.

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